A critical issue in health services research is the development and dissemination of research-tested programs to promote effective practice. Over the last two decades, a small but growing cadre of prevention programs has shown, under rigorous experimental conditions, the ability to prevent or reduce substance use and other high risk behaviors among adolescents. While extensive resources have been devoted to efficacy trials, there has been much less attention to what happens when programs are implemented in real world settings. The focus of this proposal is to determine whether and how effectiveness is compromised when prevention programs are actually adopted in the field. The study will test the effectiveness of an efficacious indicated prevention program, Reconnecting Youth (RY), which was designed to reduce high risk behaviors among adolescents. In addition, the study will assess the organizational factors affecting implementation and diffusion of the program, as well as factors affecting its generalizability and robustness. The specific aims for our project are: 1) To conduct an effectiveness trial of RY. To test program effectiveness, a randomized control trial will be conducted in two large school districts: San Francisco, CA and San Antonio, TX. 2) To conduct an organizational diffusion study of RY. Organizational factors that predict fidelity of implementation and replication of outcomes will be analyzed, using data from interviews of key school personnel, guided by the diffusion theoretical framework 3) To assess the degree of institutionalization of RY in the school districts. At the end of three semesters, implementation funding to schools will end; data collection will focus on whether and how schools continue the RY program. 4) To conduct an implementation effectiveness study of RY. Diffusion theory indicates that individual schools and districts will make significant adaptations as they institutionalize the program, and that these changes may alter program effectiveness. In order to assess implementation effectiveness, outcomes for participants will be compared to those of students in the effectiveness trial. Process evaluation data will be analyzed to assess how different school and teacher program adaptations affect outcomes.